Working with files

There are many different ways to create and/or access files. The file paths and the ways your access these files varies depending on the type of file and the location of the file.

Functions for file and folder access

Defold provides several different functions to work with files:

• You can use the standard io.* functions to read and write files. These functions give you very fine-grained control over the entire I/O process.

-- open myfile.txt for writing in binary mode
-- returns nil plus error message on failure
local f, err = io.open("path/to/myfile.txt", "wb")
if not f then
	print("Something went wrong while opening the file", err)
	return
end

-- write to the file, flush it to disk and then close the file
f:write("Foobar")
f:flush()
f:close()

-- open myfile.txt for reading in binary mode
-- returns nil plus error message on failure
local f, err = io.open("path/to/myfile.txt", "rb")
if not f then
	print("Something went wrong while opening the file", err)
	return
end

-- read the entire file as a string
-- returns nil on failure
local s = f:read("*a")
if not s then
	print("Error while reading file")
	return
end

print(s) -- Foobar

• You can use os.rename() and os.remove() to rename and remove files.

• You can use sys.save() and sys.load() to read and write Lua tables. Additional sys.* functions exist to help with platform independent file path resolution.

-- get a platform independent path to the file "highscore" for application "mygame"
local path = sys.get_save_file("mygame", "highscore")

-- save a Lua table with some data
local ok = sys.save(path, { highscore = 100 })
if not ok then
	print("Failed to save", path)
	return
end

-- load the data
local data = sys.load(path)
print(data.highscore) -- 100

File and folder locations

File and folder locations can be divided into three categories:

• Application specific files created by your application
• Files and folders bundled with your application
• System specific files accessed by your application

How to save and load application specific files

When saving and loading application specific files such as high scores, user settings and game state it is recommended to do so in a location provided by the operating system and intended specifically for this purpose. You can use sys.get_save_file() to get the OS specific absolute path to a file. Once you have the absolute path you can use the sys.*, io.* and os.* functions (see above).

Check the example showing how to use sys.save() and sys.load().

How to access files bundled with the application

You can include files with your application using bundle resources and custom resources.

Custom Resources

Custom resources are bundled in the main game archive using the Custom Resources field in game.project.

The Custom Resources field should contain a comma separated list of resources that will be included in the main game archive. If directories are specified, all files and directories in that directory are recursively included. You can read the files using sys.load_resource().

-- Load level data into a string
local data, error = sys.load_resource("/assets/level_data.json")
-- Decode json string to a Lua table
if data then
  local data_table = json.decode(data)
  pprint(data_table)
else
  print(error)
end

Bundle Resources

Bundle resources are additional files and folders located as a part of your application bundle using the Bundle Resources field in game.project.

The Bundle Resources field should contain a comma separated list of directories containing resource files and folders that should be copied as-is into the resulting package when bundling. The directories must be specified with an absolute path from the project root, for example /res. The resource directory must contain subfolders named by platform, or architecture-platform.

Supported platforms are ios, android, osx, win32, linux, web, switch A subfolder named common is also allowed, containing resource files common for all platforms. Example:

res
├── win32
│   └── mywin32file.txt
├── common
│   └── mycommonfile.txt
└── android
    ├── myandroidfile.txt
    └── res
        └── xml
            └── filepaths.xml

You can use sys.get_application_path() to get the path to where the application is stored. Use this application base path to create the final absolute path to the files you need access to. Once you have the absolute path of these files you can use the io.* and os.* functions to access the files.

local path = sys.get_application_path()
local f = io.open(path .. "/mycommonfile.txt", "rb")
local txt, err = f:read("*a")
if not txt then
	print(err)
	return
end
print(txt)

Custom and Bundle resources - comparison

System file access

Access to system files may be restricted by the operating system for security reasons. You can use the extension-directiories native extension to get the absolute path to some common system directories (ie documents, resource, temp). Once you have the absolute path of these files you can use the io.* and os.* functions to access the files (see above).

Extensions

The Asset Portal contains several assets to simplify file and folder access. Some examples:

• Lua File System (LFS) - Functions to work with directories, file permissions etc
• DefSave - A module to help you save / load config and player data between session.